Structure and Nature of Troostite

N a paper 2 presented before the Franklin Institute in the year 1924 some observations on the structure and probable nature of the constituent troostite were given. Two types of troostite were shown to occur in hardened steels depending on the mode of heat treatment. If a bar of 0.50 per cent carbon steel is given a taper heat treatment, 1 Presented by the author before W o r l d Engineering Congress, Tokio, J a p a n , October 30, 1929, 2 Lucas, " H i g h Power M e t a l l o g r a p h y -- S o m e Recent Developments in Photomicrography and Metallurgical Research," Journal of the Franklifi Institute, Vol. 201, February 1926. 101 102 BELL SYSTEM TECHNICAL JOURNAL troostite occurs which was described as flocculent border type for lack of a better designation. It seemed to be largely ferrite and appeared to be the means by which the excess constituent (in this case ferrite) appeared at the grain boundaries. If a small specimen of the same steel is heated to a high temperature and quenched in oil or water depending on the circumstances of the experiment, a structure results which may be largely martensite needles with scattered particles of troostite. Sometimes relatively large areas on the prepared surface of the specimen may be almost entirely of the constituent troostite. As is well known, this condition is controlled by the rate of cooling in the quenching operation. The type of troostite found in uniformly heated and quenched specimens was defined as nodular troostite. This paper deals further with this particular constituent of hardened steel.